Field crops are usually the targets of insect attacks. In the last few decades, there has been some substantive progress in developing more effective methods and compositions for insect invasions in crops. Chemical pesticides are relatively effective means for controlling pest invasions. However, the use of chemical pesticides also has many disadvantages. Firstly, chemical pesticides are non-selective, and as people intend to apply chemical pesticides for controlling harmful insects to a variety of crops and other plants, the chemical pesticides also cause damage to non-target organisms, such as earthworms, due to their deficiency in selectivity. Moreover, after applying chemical pesticides for a period of time, the field usually becomes barren. Chemical pesticides will be present in the environment persistently, and will usually be metabolized slowly. Such a slow metabolism results in the presence of chemical pesticide residues in the crops and environment, which will be accumulated in the food chain, particularly in the food chain of higher carnivorous animals. The accumulation of these chemical pesticides results in the induction of diseases in higher species, for example cancers in humans. Therefore, there is a strong demand for an environmentally-friendly method for controlling or eradicating insect invasions in crop production, i.e., a selective, environmentally-friendly method with biodegradability, which can also be used well in a pest resistance management system.
In the last few decades, development of an effective method for controlling plant insect pests has achieved substantive progress. Chemical pesticides are very effective for eradicating plant pests; however, these pesticides also act on non-target insects, and furthermore, chemical pesticides are present in the environment persistently, which not only causes irreversible environmental pollution, but also results in the emergence of pesticide resistant insects. Microbial pesticides, particularly pesticides obtained from the strain of Bacillus thuringiensis, abbreviated to Bt, play an important role in agricultural production as a surrogate for chemical pesticides, and have a certain insecticidal activity on insects including Lepidoptera, Diptera, Coleoptera, Hemiptera, etc. However, microbial pesticides have a relatively high requirement for the pesticide application environment, and if the environment is not suitable for the growth of these microorganisms, repeated application needs to be performed during production, and in some cases, repeated application cannot even achieve the purpose of controlling pests, thereby greatly increasing the production cost. Some transgenic plants which have enhanced resistance to the pests can be obtained by introducing one or more genes encoding Bt insecticidal proteins into the plants through genetic engineering, for example, genetically engineered maize and cotton plants capable of producing Cry toxins have been widely used in agricultural production in the USA and provide the farmers with an alternative solution of traditional pest control methods. However, the currently developed transgenic crops containing Cry toxins can only be used for preventing and controlling a narrow range of pests, and there are still no products capable of preventing and controlling piercing-sucking pests. Piercing-sucking pests are becoming major pests in developed transgenic crops due to their fast reproduction rates and wide distribution areas.
An antisense method and composition have been reported in the art and are believed to function through synthesis of a single-stranded RNA molecule (theoretically capable of hybridizing with a highly complementary sense strand of RNA molecule in vivo). It is difficult to use antisense technology in many systems for three major reasons. Firstly, an antisense sequence expressed in a transformed cell is not stable. Secondly, the instability of the antisense sequence expressed in the transformed cell accordingly results in difficulty in delivering the sequence to a host, a cell type or a biological system far away from the transgenic cell. Thirdly, with the difficulties encountered in the instability and the delivery of the antisense sequence, another difficulty is also generated for the following purpose: providing a dose capable of effectively regulating the expression level of a target sense nucleotide sequence in a recombinant cell encoding the antisense sequence.
RNA interference or RNAi is a method for downregulating gene expression in a sequence specific manner in a cell or a whole organism environment, in which the purpose of directed interference with the expression of a target gene can be achieved by the specific targeting selection and efficient mRNA repression. Although it is known in the art that the RNAi technology can be used for preventing and controlling pests, a key factor for using such a technique as a measure for controlling insect invasions is selecting the mostly suitable target gene, i.e., a gene, the function of which is lost, thereby resulting in severe disruption of the necessary biological processes and/or death of organisms. Therefore, the present invention achieves the control of insect invasions, particularly the control of insect invasions in a plant, by means of downregulating a specific target gene in a pest.